Method and apparatus for configuring bandwidth including direct current subcarrier for low cost user equipment in wireless communication system

ABSTRACT

A method and apparatus for allocating resources to a low cost user equipment (UE) in a wireless communication system is provided. A base station (BS) allocates resource blocks including a punctured direct current (DC) subcarrier to a low cost UE, and communicating with the low cost UE by using the allocated resource blocks. The allocated resource blocks may not be located at center of a set of resource blocks that the low cost UE can access at a given subframe.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2015/009837, filed on Sep. 18, 2015,which claims the benefit of U.S. Provisional Application Nos.62/052,439, filed on Sep. 18, 2014, 62/053,213, filed on Sep. 21, 2014,62/054,987, filed on Sep. 25, 2014, 62/067,970, filed on Oct. 23, 2014,62/101,390, filed on Jan. 9, 2015, 62/115,148,filed on Feb. 12, 2015,62/143,807, filed on Apr. 7, 2015, 62/153,494, filed on Apr. 27, 2015,and 62/166,641, filed on May 26, 2015, the contents of which are allhereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for configuring a bandwidthincluding a direct current (DC) subcarrier for a low cost user equipment(UE) in a wireless communication system.

Related Art

3rd generation partnership project (3GPP) long-term evolution (LTE) is atechnology for enabling high-speed packet communications. Many schemeshave been proposed for the LTE objective including those that aim toreduce user and provider costs, improve service quality, and expand andimprove coverage and system capacity. The 3GPP LTE requires reduced costper bit, increased service availability, flexible use of a frequencyband, a simple structure, an open interface, and adequate powerconsumption of a terminal as an upper-level requirement.

In the future versions of the LTE-A, it has been considered to configurelow-cost/low-end (or, low-complexity) user equipments (UEs) focusing onthe data communication, such as meter reading, water level measurement,use of security camera, vending machine inventory report, etc. Forconvenience, these UEs may be called machine type communication (MTC)UEs. Since MTC UEs have small amount of transmission data and haveoccasional uplink data transmission/downlink data reception, it isefficient to reduce the cost and battery consumption of the UE accordingto a low data rate. Specifically, the cost and battery consumption ofthe UE may be reduced by decreasing radio frequency (RF)/basebandcomplexity of the MTC UE significantly by making the operating frequencybandwidth of the MTC UE smaller.

Accordingly, a method for supporting a base station, which operates inrelatively wider bandwidth with conventional UEs, to perform datatransmission/reception with the MTC UE, which operates in a narrowerbandwidth, may be required.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for using asmaller bandwidth for a low cost user equipment (UE) in a wirelesscommunication system. The present invention discusses how tocreate/handle a UE with limited radio frequency (RF) capability toreceive downlink data successfully serviced by a wideband systembandwidth network. The present invention provides a method and apparatusfor determining which part of system bandwidth is accessible by a lowcost UE. The present invention provides a method and apparatus forallocating resource blocks for a UE with reduced bandwidth.

In an aspect, a method for allocating, by a base station (BS), resourcesto a low cost user equipment (UE) in a wireless communication system isprovided. The method includes allocating resource blocks including apunctured direct current (DC) subcarrier to a low cost UE, andcommunicating with the low cost UE by using the allocated resourceblocks.

In another aspect, a base station (BS) includes a memory, a transceiver,and a processor coupled to the memory and the transceiver, andconfigured to allocate resource blocks including a punctured directcurrent (DC) subcarrier to a low cost user equipment (UE), and controlthe transceiver to communicate with the low cost UE by using theallocated resource blocks.

Low cost UE can be supported efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows structure of a radio frame of 3GPP LTE.

FIG. 3 shows a resource grid for one downlink slot.

FIG. 4 shows structure of a downlink subframe.

FIG. 5 shows structure of an uplink subframe.

FIG. 6 shows an example of a set of PRBs accessible by a low cost UEaccording to an embodiment of the present invention.

FIG. 7 shows another example of a set of PRBs accessible by a low costUE according to an embodiment of the present invention.

FIG. 8 shows another example of a set of PRBs accessible by a low costUE according to an embodiment of the present invention.

FIG. 9 shows another example of a set of PRBs accessible by a low costUE according to an embodiment of the present invention.

FIG. 10 shows another example of a set of PRBs accessible by a low costUE according to an embodiment of the present invention.

FIG. 11 shows another example of a set of PRBs accessible by a low costUE according to an embodiment of the present invention.

FIG. 12 shows another example of a set of PRBs accessible by a low costUE according to an embodiment of the present invention.

FIG. 13 shows an example of a center narrowband according to anembodiment of the present invention.

FIG. 14 shows another example of a center narrowband according to anembodiment of the present invention.

FIG. 15 shows another example of a center narrowband according to anembodiment of the present invention.

FIG. 16 shows an example of CRS RE mapping to subDLBW other than center6 PRBs according to an embodiment of the present invention.

FIG. 17 shows another example of CRS RE mapping to subDLBW other thancenter 6 PRBs according to an embodiment of the present invention.

FIG. 18 shows an example of Vshift for CRS depending on a DC subcarrieraccording to an embodiment of the present invention.

FIG. 19 shows another example of Vshift for CRS depending on a DCsubcarrier according to an embodiment of the present invention.

FIG. 20 shows an example of a RB allocation with artificial DCsubcarrier according to an embodiment of the present invention.

FIG. 21 shows another example of a RB allocation with artificial DCsubcarrier according to an embodiment of the present invention.

FIG. 22 shows another example of a RB allocation with artificial DCsubcarrier according to an embodiment of the present invention.

FIG. 23 shows another example of a RB allocation with artificial DCsubcarrier according to an embodiment of the present invention.

FIG. 24 shows another example of a RB allocation with artificial DCsubcarrier according to an embodiment of the present invention.

FIG. 25 shows an example of relationship between channel bandwidth andtransmission bandwidth.

FIG. 26 shows an example of fragmented segments according to anembodiment of the present invention.

FIG. 27 shows an example of a method for allocating resources to a lowcost UE according to an embodiment of the present invention.

FIG. 28 shows another example of a method for allocating resources to alow cost UE according to an embodiment of the present invention.

FIG. 29 shows a wireless communication system to implement an embodimentof the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Techniques, apparatus and systems described herein may be used invarious wireless access technologies such as code division multipleaccess (CDMA), frequency division multiple access (FDMA), time divisionmultiple access (TDMA), orthogonal frequency division multiple access(OFDMA), single carrier frequency division multiple access (SC-FDMA),etc. The CDMA may be implemented with a radio technology such asuniversal terrestrial radio access (UTRA) or CDMA2000. The TDMA may beimplemented with a radio technology such as global system for mobilecommunications (GSM)/general packet radio service (GPRS)/enhanced datarates for GSM evolution (EDGE). The OFDMA may be implemented with aradio technology such as institute of electrical and electronicsengineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20,evolved-UTRA (E-UTRA) etc. The UTRA is a part of a universal mobiletelecommunication system (UMTS). 3rd generation partnership project(3GPP) long term evolution (LTE) is a part of an evolved-UMTS (E-UMTS)using the E-UTRA. The 3GPP LTE employs the OFDMA in downlink (DL) andemploys the SC-FDMA in uplink (UL). LTE-advance (LTE-A) is an evolutionof the 3GPP LTE. For clarity, this application focuses on the 3GPPLTE/LTE-A. However, technical features of the present invention are notlimited thereto.

FIG. 1 shows a wireless communication system. The wireless communicationsystem 10 includes at least one evolved NodeB (eNB) 11. Respective eNBs11 provide a communication service to particular geographical areas 15a, 15 b, and 15 c (which are generally called cells). Each cell may bedivided into a plurality of areas (which are called sectors). A userequipment (UE) 12 may be fixed or mobile and may be referred to by othernames such as mobile station (MS), mobile terminal (MT), user terminal(UT), subscriber station (SS), wireless device, personal digitalassistant (PDA), wireless modem, handheld device. The eNB 11 generallyrefers to a fixed station that communicates with the UE 12 and may becalled by other names such as base station (BS), base transceiver system(BTS), access point (AP), etc.

In general, a UE belongs to one cell, and the cell to which a UE belongsis called a serving cell. An eNB providing a communication service tothe serving cell is called a serving eNB. The wireless communicationsystem is a cellular system, so a different cell adjacent to the servingcell exists. The different cell adjacent to the serving cell is called aneighbor cell. An eNB providing a communication service to the neighborcell is called a neighbor eNB. The serving cell and the neighbor cellare relatively determined based on a UE.

This technique can be used for DL or UL. In general, DL refers tocommunication from the eNB 11 to the UE 12, and UL refers tocommunication from the UE 12 to the eNB 11. In DL, a transmitter may bepart of the eNB 11 and a receiver may be part of the UE 12. In UL, atransmitter may be part of the UE 12 and a receiver may be part of theeNB 11.

The wireless communication system may be any one of a multiple-inputmultiple-output (MIMO) system, a multiple-input single-output (MISO)system, a single-input single-output (SISO) system, and a single-inputmultiple-output (SIMO) system. The MIMO system uses a plurality oftransmission antennas and a plurality of reception antennas. The MISOsystem uses a plurality of transmission antennas and a single receptionantenna. The SISO system uses a single transmission antenna and a singlereception antenna. The SIMO system uses a single transmission antennaand a plurality of reception antennas. Hereinafter, a transmissionantenna refers to a physical or logical antenna used for transmitting asignal or a stream, and a reception antenna refers to a physical orlogical antenna used for receiving a signal or a stream.

FIG. 2 shows structure of a radio frame of 3GPP LTE. Referring to FIG.2, a radio frame includes 10 subframes. A subframe includes two slots intime domain. A time for transmitting one subframe is defined as atransmission time interval (TTI). For example, one subframe may have alength of 1 ms, and one slot may have a length of 0.5 ms. One slotincludes a plurality of orthogonal frequency division multiplexing(OFDM) symbols in time domain. Since the 3GPP LTE uses the OFDMA in theDL, the OFDM symbol is for representing one symbol period. The OFDMsymbols may be called by other names depending on a multiple-accessscheme. For example, when SC-FDMA is in use as a UL multi-access scheme,the OFDM symbols may be called SC-FDMA symbols. A resource block (RB) isa resource allocation unit, and includes a plurality of contiguoussubcarriers in one slot. The structure of the radio frame is shown forexemplary purposes only. Thus, the number of subframes included in theradio frame or the number of slots included in the subframe or thenumber of OFDM symbols included in the slot may be modified in variousmanners.

The wireless communication system may be divided into a frequencydivision duplex (FDD) scheme and a time division duplex (TDD) scheme.According to the FDD scheme, UL transmission and DL transmission aremade at different frequency bands. According to the TDD scheme, ULtransmission and DL transmission are made during different periods oftime at the same frequency band. A channel response of the TDD scheme issubstantially reciprocal. This means that a DL channel response and a ULchannel response are almost the same in a given frequency band. Thus,the TDD-based wireless communication system is advantageous in that theDL channel response can be obtained from the UL channel response. In theTDD scheme, the entire frequency band is time-divided for UL and DLtransmissions, so a DL transmission by the eNB and a UL transmission bythe UE cannot be simultaneously performed. In a TDD system in which a ULtransmission and a DL transmission are discriminated in units ofsubframes, the UL transmission and the DL transmission are performed indifferent subframes.

FIG. 3 shows a resource grid for one downlink slot. Referring to FIG. 3,a DL slot includes a plurality of OFDM symbols in time domain. It isdescribed herein that one DL slot includes 7 OFDM symbols, and one RBincludes 12 subcarriers in frequency domain as an example. However, thepresent invention is not limited thereto. Each element on the resourcegrid is referred to as a resource element (RE). One RB includes 12×7resource elements. The number N^(DL) of RBs included in the DL slotdepends on a DL transmit bandwidth. The structure of a UL slot may besame as that of the DL slot. The number of OFDM symbols and the numberof subcarriers may vary depending on the length of a CP, frequencyspacing, etc. For example, in case of a normal cyclic prefix (CP), thenumber of OFDM symbols is 7, and in case of an extended CP, the numberof OFDM symbols is 6. One of 128, 256, 512, 1024, 1536, and 2048 may beselectively used as the number of subcarriers in one OFDM symbol.

FIG. 4 shows structure of a downlink subframe. Referring to FIG. 4, amaximum of three OFDM symbols located in a front portion of a first slotwithin a subframe correspond to a control region to be assigned with acontrol channel. The remaining OFDM symbols correspond to a data regionto be assigned with a physical downlink shared chancel (PDSCH). Examplesof DL control channels used in the 3GPP LTE includes a physical controlformat indicator channel (PCFICH), a physical downlink control channel(PDCCH), a physical hybrid automatic repeat request (HARQ) indicatorchannel (PHICH), etc. The PCFICH is transmitted at a first OFDM symbolof a subframe and carries information regarding the number of OFDMsymbols used for transmission of control channels within the subframe.The PHICH is a response of UL transmission and carries a HARQacknowledgment (ACK)/non-acknowledgment (NACK) signal. Controlinformation transmitted through the PDCCH is referred to as downlinkcontrol information (DCI). The DCI includes UL or DL schedulinginformation or includes a UL transmit (Tx) power control command forarbitrary UE groups.

The PDCCH may carry a transport format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a paging channel(PCH), system information on the DL-SCH, a resource allocation of anupper-layer control message such as a random access response transmittedon the PDSCH, a set of Tx power control commands on individual UEswithin an arbitrary UE group, a Tx power control command, activation ofa voice over IP (VoIP), etc. A plurality of PDCCHs can be transmittedwithin a control region. The UE can monitor the plurality of PDCCHs. ThePDCCH is transmitted on an aggregation of one or several consecutivecontrol channel elements (CCEs). The CCE is a logical allocation unitused to provide the PDCCH with a coding rate based on a state of a radiochannel. The CCE corresponds to a plurality of resource element groups.

A format of the PDCCH and the number of bits of the available PDCCH aredetermined according to a correlation between the number of CCEs and thecoding rate provided by the CCEs. The eNB determines a PDCCH formataccording to a DCI to be transmitted to the UE, and attaches a cyclicredundancy check (CRC) to control information. The CRC is scrambled witha unique identifier (referred to as a radio network temporary identifier(RNTI)) according to an owner or usage of the PDCCH. If the PDCCH is fora specific UE, a unique identifier (e.g., cell-RNTI (C-RNTI)) of the UEmay be scrambled to the CRC. Alternatively, if the PDCCH is for a pagingmessage, a paging indicator identifier (e.g., paging-RNTI (P-RNTI)) maybe scrambled to the CRC. If the PDCCH is for system information (morespecifically, a system information block (SIB) to be described below), asystem information identifier and a system information RNTI (SI-RNTI)may be scrambled to the CRC. To indicate a random access response thatis a response for transmission of a random access preamble of the UE, arandom access-RNTI (RA-RNTI) may be scrambled to the CRC.

FIG. 5 shows structure of an uplink subframe. Referring to FIG. 5, a ULsubframe can be divided in a frequency domain into a control region anda data region. The control region is allocated with a physical uplinkcontrol channel (PUCCH) for carrying UL control information. The dataregion is allocated with a physical uplink shared channel (PUSCH) forcarrying user data. When indicated by a higher layer, the UE may supporta simultaneous transmission of the PUSCH and the PUCCH. The PUCCH forone UE is allocated to an RB pair in a subframe. RBs belonging to the RBpair occupy different subcarriers in respective two slots. This iscalled that the RB pair allocated to the PUCCH is frequency-hopped in aslot boundary. This is said that the pair of RBs allocated to the PUCCHis frequency-hopped at the slot boundary. The UE can obtain a frequencydiversity gain by transmitting UL control information through differentsubcarriers according to time.

UL control information transmitted on the PUCCH may include a HARQACK/NACK, a channel quality indicator (CQI) indicating the state of a DLchannel, a scheduling request (SR), and the like. The PUSCH is mapped toa UL-SCH, a transport channel. UL data transmitted on the PUSCH may be atransport block, a data block for the UL-SCH transmitted during the TTI.The transport block may be user information. Or, the UL data may bemultiplexed data. The multiplexed data may be data obtained bymultiplexing the transport block for the UL-SCH and control information.For example, control information multiplexed to data may include a CQI,a precoding matrix indicator (PMI), an HARQ, a rank indicator (RI), orthe like. Or the UL data may include only control information.

In the current LTE specification, all UEs shall support maximum 20 MHzsystem bandwidth, which requires baseband processing capability tosupport 20 MHz bandwidth. To reduce hardware cost and battery power ofthe UE used for machine type communication (MTC), reducing bandwidth isa very attractive option. To enable narrow-band MTC UEs, the current LTEspecification shall be changed to allow narrow-band UE category. If theserving cell has small system bandwidth (smaller than or equal tobandwidth that narrow-band UE can support), the UE can attach based onthe current LTE specification.

Hereinafter, a method for supporting a base station, which operates inrelatively wider bandwidth with conventional UEs, to perform datatransmission/reception with the MTC UE, according to an embodiment ofthe present invention is described. Hereinafter, all of a MTC UE, a lowcost UE, a low end UE, a low complexity UE, a narrow(er) band UE, asmall(er) band UE, or a new category UE may be used mixed with eachother. Or, just UE may refer one of UEs described above. In thedescription below, a case where system bandwidth of available cells islarger than bandwidth that new category narrow-band UEs can support maybe assumed. For the new category UE, it may be assumed that only onenarrow-band is defined. In other words, all narrow band UE shall supportthe same narrow bandwidth smaller than 20 MHz. It may be assumed thatthe narrow bandwidth is larger than 1.4 MHz (6 RB). However, the presentinvention can be applied to narrower bandwidth less than 1.4 MHz as well(e.g. 200 kHz), without loss of generality.

The followings may be assumed:

(1) Operating bandwidth of a UE may be known to the eNB. To informoperating bandwidth, multiple approaches may be proposed. It may beassumed that that before scheduling any PDSCH/PUSCH, the eNB knows theoperating bandwidth of a UE. In the description below, operatingbandwidth in terms of the number of PRBs of a narrow band UE is given asN_(RB) ^(DL) ^(_) ^(Op). It may be assumed that operating bandwidth isconsistent for all narrow band UEs within a cell. Also, UL transmissionbandwidth of a narrow band UE may be the same as the DL operatingbandwidth, i.e. N_(RB) ^(DL) ^(_) ^(Op)In other words, UL (RF and)baseband can process only narrow band as well.

(2) Operating bandwidth of a UE may be equal to or larger than 1.4 MHz(or 6 RB), and thus, the UE is able to receive physical broadcastchannel (PBCH)/primary synchronization signal (PSS)/secondarysynchronization signal (SSS) transmitted over center 6 RB of systemfrequency band. Otherwise, a new signal similar to PBCH/PSS/SSS may betransmitted to narrower bandwidth. Even with supporting 1.4 MHz, it maybe expected that a new signal for PBCH/PSS/SSS are considered to supporta low cost UE. In this case, the new signal may be called MTC-PBCH,MTC-PSS and MTC-SSS.

(3) The present invention may be applied two scenarios: (1) RF iscapable of receiving system bandwidth (e.g., 20 MHz) but baseband iscapable of processing only narrowband, (2) both RF and baseband canhandle narrow bandwidth. If the first scenario is used, frequencyretuning delay is not considered. If the second scenario is used, tuningdelay to change frequency should be considered.

(4) This invention may assume that via RRC signaling (or other means)the UE is notified the number of symbols used for legacy PDCCH (sentover system bandwidth) after serving cell is established. At initialstage, upon receiving PBCH (i.e. discovering system bandwidth), thenarrow band UE may configure the default value for the number of symbolsfor legacy PDCCH to the maximum symbol counts based on system bandwidth(e.g. three for NRBDL=100).

(5) The narrow band UE may support only one LTE band and single radioaccess technology (RAT). However, it is not precluded to considerinter-RAT handover case for a low cost UE. Just for the simplicity, thisinvention may assume single-RAT supporting UE.

(6) As the narrow-band UE cannot decode legacy PDCCH, another controlchannel mechanism (such as enhanced PDCCH transmitted/multiplexed inPDSCH area) may be assumed for supporting narrow band UEs.

Which part of system bandwidth is accessible by the low cost UEaccording to an embodiment of the present invention is described.Assuming that the system bandwidth is larger than the bandwidthsupported by the low cost UE, it needs to be clarified which part ofsystem bandwidth is accessed by the low cost UE. For example, systembandwidth is N and the low cost UE can support M (where N>M), at leastone of the following approaches may be considered.

(1) Only center M MHz (or K kHz) may be used by the low cost UE.Regardless of the number of low cost UEs, only center M MHz (or K kHz)may be used. To maximize multiplexing among low cost UEs, time divisionmultiplexing (TDM) between low cost UEs may be considered, where asubset of subframes allocated to each low cost UE is indicated viahigher layer signaling or SIB or PBCH. Another approach is to allocatedifferent subframes to different low cost UEs based on a predeterminedrule. Similar to device-to-device (D2D) communication, a set of resourcepool which can be used by low cost UEs may be signaled via SIB whereeach low cost UE may claim which pool to use via RRC signaling to thenetwork upon RRC connection.

(2) N MHz can be partitioned to K subDLBWs, where each subDLBW is M MHz.Hereinafter, subDLBW refers a set of PRBs (or bandwidth) that a low costUE can access at a given subframe. Each subDLBW may transmit individualsynchronization signals, such as MTC-PSS/MTC-SSS, such that a UE, oncediscovers a subDLBW, will stay in that subDLBW. Or, the center subDLBWor one dedicated subDLBW may be used for cell association procedure suchas reading synchronization signal, random access channel (RACH)procedure, etc. The frequency used for DL and UL for narrowband UEs maybe different. Once the connection is established, the subDLBW may bedetermined by C-RNTI assigned to the UE. Alternatively, each UE or thenetwork may determine a subDLBW based on scanning each channel, or basedon channel state information (CSI) which is signaled via higher layersignaling. Alternatively, random access response (RAR) may carry theinformation on subDLBW which will be used by a UE (which has transmittedthe preamble corresponding to the RAR). Once subDLBW is indicated by theRAR, a UE may jump to the subDLBW and transmit PUSCH. It is assumed thatDL subDLBW and UL subDLBW may be preconfigured or configured by higherlayer. Or, the UL subDLBW may be indicated by DCI only where the UE mayignore PRB allocation which may not fit in its RF bandwidth or basebandprocessing capability (for example, 8 PRBs are assigned, whereas the UEonly supports 6 PRB PUSCH transmission, then 2 PRBs outside of itsoperating PRB may be ignored or the total grant may be ignored).

(3) A dedicated subDLBW may be assigned. Even though a low cost UEaccesses only one subDLBW, the subDLBW may not in the center of thesystem bandwidth. It may be assigned somewhere else. However from the UEperspective, there is no need to differentiate the dedicated subDLBWfrom 1.4 MHz bandwidth carrier (in other words, no need of separateimplementation is needed to support the dedicated subDLBW if it is notin center), if the low cost UE supports 1.4 MHz bandwidth carrier. Ifthe low cost UE is not capable of reading legacy synchronizationsignals, it may not differentiate one dedicated subDLBW from another onein terms of synchronization and cell detection. In other words, thenetwork may be allowed to setup a different dedicated subDLBW in anyfrequency (aligned with low cost UE's channel raster) which will bediscovered via cell detection procedure.

(4) Another option to determine the available subDLBW is to assume thata set of K subDLBWs is available based on a predetermined rule, similarto physical random access channel (PRACH) resource. For example,start_offset (n_(PRB offset) ^(NB)) and K (f_(NB)) may be configured(either by master information block (MIB), SIB, or higher layersignaling), where the subDLBWs are defined as Equation 1 or Equation 2.

$\begin{matrix}{n_{PRB}^{NB} = \left\{ \begin{matrix}{{n_{{PRB}\mspace{14mu}{offset}}^{NB} + {6\left\lfloor \frac{f_{NB}}{2} \right\rfloor}},} & {{{if}\mspace{14mu} f_{NB}{mod}\; 2} = 0} \\{{N_{RB}^{DL} - 6 - n_{{PRB}\mspace{14mu}{offset}}^{NB} - {6\left\lfloor \frac{f_{NB}}{2} \right\rfloor}},} & {otherwise}\end{matrix} \right.} & {< {{Equation}\mspace{14mu} 1} >}\end{matrix}$

By Equation 1, subDLBWs may be placed from the edge except for theoffset PRBs.

$\begin{matrix}{n_{PRB}^{NB} = \left\{ \begin{matrix}{{n_{{PRB}\mspace{14mu}{offset}}^{NB} + {6\left\lfloor \frac{f_{NB}}{2} \right\rfloor}},} & {{{if}\mspace{14mu} f_{NB}{mod}\; 2} = 0} \\{{N_{RB}^{DL} - 6 - {6\left\lfloor \frac{f_{NB}}{2} \right\rfloor}},} & {otherwise}\end{matrix} \right.} & {< {{Equation}\mspace{14mu} 2} >}\end{matrix}$

By Equation 2, the offset is assume only in one direction. The equationsshown above are based on the assumption that the number of PRBs used fornarrowband is 6 PRBs. However, the principle may be applicable to anylower number of PRBs or larger number of PRBs allocated to a subDLBW. Ifone PRB size is used, the index of PRB may be used or only a subset ofPRBs may be used with indexing within the subset.

Determination of possible K according to an embodiment of the presentinvention is described. It may be assumed that in terms of signalingwhich subDLBW is used, a UE is indicated by an index i out of K. Thedetermination of K may be based on the at least one of followings.

(1) MTC-PBCH or MTC-SIB may inform the list of subDLBWs along with K. Interms of signaling for the list of subDLBWs, it may include the centerfrequency, or the PRB index where direct current (DC) subcarrier mayreside and the subcarrier index which will be assumed as a DC subcarrierfor each subDLBW. Additionally, it may also include the bandwidth ofsubDLBW. Indication of which subDLBW will be used may be signaledadditionally by higher layer signaling. Alternatively, indication ofwhich subDLBW may be determined implicitly based on C-RNTI or temporaryC-RNTI.

(2) MTC-PBCH or MTC-SIB may inform start_offset (n_(PRB offset) ^(NB))and K (f_(NB)) such that a set of subDLBWs can be formed automatically.More specifically, the values from MTC-PBCH may only indicate subDLBWswhich will be used for cell broadcast data such as SIB, paging, RAR,etc. By MTC-SIB or higher layer signaling, a set of subDLBW used forunicast transmission may also be configured. In terms of offset, theoffset value may be 0 or 1, where 0 means no offset and 1 means offsetof 6 PRBs or K PRB(s) (K is the size of one subDLBW). In other words,subDLBW may be formed without assuming any offset from the PRB 0,whereas, if needed, offset of 6 PRBs or K PRB(s) (K is the size of onesubDLBW) is configured. This is to minimize the signaling overhead.

(3) Predetermined set of K subDLBWs may be configured, where K isdetermined based on the system bandwidth. In this case, even thoughsubDLBW may be predetermined based on system bandwidth, the subcarrierindex which will be used for DC subcarrier may be further signaled. Itmay be common for K subDLBWs or an individual signaling of DC subcarriermay also be considered. Indication of which subDLBW will be used may besignaled additionally by higher layer signaling. Alternatively,indication of which subDLBW may be determined implicitly based on C-RNTIor temporary C-RNTI.

(4) Higher layer signaling may inform the list of subDLBWs along with K.In terms of signaling for the list of subDLBWs, it may include thecenter frequency, or the PRB index where DC subcarrier may reside andthe subcarrier index which will be assumed as a DC subcarrier for eachsubDLBW. Additionally, it may also include the bandwidth of subDLBW.Indication of which subDLBW will be used may be signaled additionally byhigher layer signaling. Alternatively, indication of which subDLBW maybe determined implicitly based on C-RNTI or temporary C-RNTI.

(5) Media access control (MAC) control element (CE) and/or dynamic DCImay inform the list of subDLBWs along with K. In this case, DCI mayindicate a subset of K subDLBWs used by the network for a low cost UE,out of potentially M subDLBWs feasible in a system bandwidth. In thiscase, the list of M subDLBWs may be higher layer configured, orbroadcasted by SIB or predetermined (by one of the above approaches). Inthis case, additional DCI or the same DCI may indicate the subDLBW viaresource allocation for PDSCH. In other words, if a UE is assigned withdifferent resource from where the control signal is received, it mayswitch to different subDLBW to read data. Given that a UE may not beable to read different frequency within a subframe, if this is used,cross-subframe scheduling may be used. Alternatively, additional DCI orthe same DCI may indicate the subDLBW which will be used in a nextsubframe. Based on grouping of UEs, for each group, separate DCI may betransmitted to indicate which subDLBW will be used. This DCI may betransmitted periodically. If DCI is not received, the UE may fallback tocenter subDLBW or use the previously assigned subDLBW.

(6) Paging may indicate the list of subDLBWs. Assuming that only thepaging is received at a predetermined subDLBW, paging may indicate thelist of subDLBWs. Paging may also indicate the subDLBW used by the UEreceiving the paging. In terms of signaling for the list of subDLBWs, itmay include the center frequency, or the PRB index where DC subcarriermay reside and the subcarrier index which will be assumed as a DCsubcarrier for each subDLBW. Additionally, it may also include thebandwidth of subDLBW.

In terms of indication of subband to be used for the low cost UE, if aUE is not either configured with C-RNTI or temporary C-RNTI, it may befurther assumed that an identifier (such as factory-set low cost ID) maybe used to determine the subband. This may be applied if the list ofsubbands are transmitted by the SIB or PBCH or if a set ofsubDLBWs/subULBWs are predetermined based on system bandwidth. SincePBCH transmits system bandwidth, it may be considered that the list ofsubbands are indicated by PBCH. Furthermore, whether to use subDLBWs (ifpredetermined set is used if subDLBW is used) or not may be signaled viaSIB or PBCH. In this case, the subband indicates the DL which may alsobe used for any successive SIB transmission (in this case, the networkmay transmit synchronization and common channels in multiple subbands)as well as UL where PRACH may be transmitted in that UL subband ratherthan a center 6 PRBs. The mapping between UL subbands corresponding toDL subbands may be predetermined, or a set of UL subbands may also beindicated by the network via PBCH, or SIB or RAR or higher layersignaling. For the simplicity, it may be assumed that the samesubcarrier indices for DL and UL for a subband may be assumed. This isstraightforward in case of TDD. In case of FDD, in the matched ULspectrum which has the same system bandwidth as DL, UL subcarriers maymatch to the DL subcarriers by one-to-one starting from the lowestsubcarrier index/frequency of UL and DL, respectively.

How to create subDLBW and/or subULBW according to an embodiment of thepresent invention is described. More than one subDLBW may utilize onesubcarrier. In other words, a subDLBW for a UE may be overlapped withanother subDLBW for another UE. A UE supporting reduced bandwidth is notrequired to monitor more than one subDLBW at a given TTI. However, itwould be up to the UE whether to monitor other subDLBW or not. Thisincludes DL monitoring as well as for measurements.

For example, if 8 PRBs may be used for low cost UEs, a set of UEs may beassigned with first 6 PRBs, whereas a different set of UEs may beassigned with the last 6 PRBs. If this is used, 4 PRBs may be overlappedbetween two subDLBWs. In this case, a UE may assume that cell-commonchannels are transmitted based on the system bandwidth rather than basedon 6 PRBs. If PDCCH for two sets of UEs are shared, either PDCCH may bescheduled only in the overlapped PRBs (i.e. the overlapped 4 PRBs). Inthis case, the PRBs used for PDCCH needs to be higher layer configuredvia RRC signaling or via SIB or PBCH.

Alternatively, the PRBs used for PDCCH may be limited to one or a fewPRBs regardless of a location of subDLBW, where the location of PDCCHmay be prefixed (e.g. at the first PRB or the last PRB, or distributedacross 6 PRBs). More specifically, this may be applied only for PDCCH atcommon search space (CSS), whereas PDCCH at USS may be separate(configured separately per UE or per group). This may be particularlyuseful when system bandwidth is larger than 6 PRBs, and thus, 6 PRBs maynot be aligned with RB group (RBG) or PRB group (PRG). Since it isassumed that the same pre-coding is used for PRG, it is also desirableto consider subDLBWs aligned with PRG for legacy UEs.

It is not desirable to schedule both legacy UE and the low cost UE inthe same PRG, if demodulation reference signal (DM-RS) basedtransmission is used (at least for legacy UE). For example, if thesystem bandwidth is 100 PRBs, and the RBG size is 4 PRBs per RBG, thentotally 25 RBGs are available in the system. If center 6 PRBs are usedfor low cost UEs, it will use the center 4 PRBs (from 13th RBG) and 1PRB from the adjacent PRBs, thus, 3 PRBs from the adjacent 2 RBGs maynot be used (or not schedulable) to legacy UEs. In this case, total 12PRBs may be utilized for the low cost UEs. To utilize those adjacent 2RBGs, two 6 PRBs orthogonal subDLBWs may be formed. Or overlappedsubDLBWs may be formed to allow some overlap between subDLBWs.

If overlapped subDLBW is used, utilizing PDCCH becomes a bitchallenging. For that, a UE may be higher layer configured with a set ofPRBs used for PDCCH (along with potential OFDM symbols) or SIB or PBCHmay indicate the set of PRBs used for PDCCH. It is also expected that anew control channel is used for a low cost UE, which may be called asMTC-PDCCH. For MTC-PDCCH, the approaches of enhanced PDCCH (EPDCCH)and/or PDCCH may be applied. In general, the set of PRBs and the numberof OFDM symbols used for MTC-PDCCH may be signaled by higher layer orvia RAR or SIB or PBCH. Considering this, if cross-subframe schedulingis used or the frequency retuning time is marginal, the subDLBW whichtransmits PDCCH may be different from subDLBW which schedules PDSCH. InTDD, subDLBW frequency for PDCCH may be different from subULBW frequencyfor PUSCH transmission as well. By this, multiple DCIs of multiple UEsmay be multiplexed, whereas data may be distributed across all PRBswhich can be allocated to low cost UEs. In this sense, control channelsfor MTC may be multiplexed by frequency division multiplexing (FDM)rather than TDM, where control channels for a UE and control channelsfor another UE may be shared in different frequency (similar to EPDCCH).

In terms of UL subULBW corresponding to DL subDLBW, a straightforwardrule may be to map one-to-one. In TDD, the same frequency may be usedfor DL subDLBW and UL subULBW. Thus, without any additional signaling ofUL subULBW, a UE may assume that the same frequency resource of DLsubDLBW is used for UL subULBW. Otherwise, higher layer signaling or SIBmay indicate the mapping between subDLBW and subULBW. For example,offset of subcarrier between subDLBW and subULBW may be assigned suchthat (starting of subULBW=starting subcarrier of subDLBW+offset). Ingeneral, a set of subDLBWs and a set of subULBWs may be indicatedseparately. If separate configuration is given, the mapping may also beindicated by higher layer signaling or RAR or SIB or PBCH. For FDD,assuming that the DL-UL gap is K MHz, the frequency of starting ofsubDLBW+K MHz may become the frequency for the starting of subULBW.

When K is pre-determined, how to define a subDLBW according to anembodiment of the present invention is described. To determine PRBs usedfor a subDLBW, at least one of following approaches may be considered.

(1) Lowest indexed PRBs or highest indexed PRBs may be used first for asubDLBW. To determine where to put DC subcarrier in terms of RB out of NRBs (which is based on the DL system bandwidth instead of by bandwidththat a low cost UE can support), the lowest indexed RBs (6 PRBs+1subcarrier or 6 PRBs) and the highest indexed RBs (6 PRBs+1 subcarrieror 6 PRBs) may be used for 1.4 MHz transmission bandwidth (6 PRBs),where the DC subcarrier comes in the center RB. If more than one subDLBWis used, the next 6 PRBs+1 subcarrier may be determined as a subDLBW.For example, if the system bandwidth is 10 MHz, i.e. the number of PRBsis 50, the first 6 PRBs+1 subcarrier [PRB 0-6] is used for the firstsubDLBW, [PRB 6-12] is used the second subDLBW. A gap between subDLBWsmay be considered. In that case, a predetermined gap may be consideredbetween subbands. The subband PRB may be aligned with PRB mapping of thesystem bandwidth. In other words, the start and end of a subband may bealigned with start and end of PRB boundaries.

(2) PRBs used for a subDLBW may be determined starting from the center.6 PRBs (3 PRBs/DC subcarrier/3 PRBs) may be the first subDLBW. Thesecond subDLBW may be defined as the next 6 PRBs+1 subcarrier.

(3) PRBs used for a subDLBW may be aligned with RBG for each systembandwidth. For example, for 3 MHz, the size of RBG is 2, and thus, toallow at least one RBG being intact, rather than starting from thelowest index PRB, it may start at 3rd with 3 MHz system bandwidth.

(4) PRBs used for a subDLBW may be determined starting from the edgePRBs first. For example, if the system bandwidth is 100 PRBs, the first6 PRBs may form the first subband, the last 6 PRBs may form the secondsubband, the next lowest 6 PRBs may form the third subband, and so on.

FIG. 6 shows an example of a set of PRBs accessible by a low cost UEaccording to an embodiment of the present invention. It is assumed thatM=1.4 MHz, N=3 MHz, and center 6 PRBs are used for 1 subDLBW. In thiscase, K=1. Referring to FIG. 6, center 6 PRBs or 6 PRBs+1 subcarrier isassigned for a subDLBW.

FIG. 7 shows another example of a set of PRBs accessible by a low costUE according to an embodiment of the present invention. It is assumedthat M=1.4 MHz, N=3 MHz, and center 6 PRBs are not used. In this case, Kmay be 2. Referring to FIG. 7, the lowest indexed PRBs and the highestindexed PRBs are assigned for 2 subDLBWs.

FIG. 8 shows another example of a set of PRBs accessible by a low costUE according to an embodiment of the present invention. It is assumedthat M=1.4 MHz, N=3 MHz, and center 6 PRBs are not used. In this case, Kmay be 2. Referring to FIG. 8, legacy UEs may be assigned to the lowestindexed PRBs, and the highest indexed PRBs are assigned for 2 subDLBWswith consideration of alignment of RBS.

FIG. 9 shows another example of a set of PRBs accessible by a low costUE according to an embodiment of the present invention. It is assumedthat M=1.4 MHz, N=5 MHz, and center 6 PRBs are used for 1 subDLBW.Referring to FIG. 9, K=1 and center 6 PRBs or 6 PRBs+1 subcarrier isassigned for a subDLBW.

FIG. 10 shows another example of a set of PRBs accessible by a low costUE according to an embodiment of the present invention. It is assumedthat M=1.4 MHz, N=5 MHz, and center PRBs are used for multiple subDLBWs.Referring to FIG. 10, K=3 and center PRBs are assigned for 3 subDLBWs.

FIG. 11 shows another example of a set of PRBs accessible by a low costUE according to an embodiment of the present invention. It is assumedthat M=1.4 MHz, N=5 MHz, and center 6 PRBs are not used. Referring toFIG. 11, K=4 and the lowest indexed PRBs and the highest indexed PRBsare assigned for 4 subDLBWs.

FIG. 12 shows another example of a set of PRBs accessible by a low costUE according to an embodiment of the present invention. It is assumedthat M=1.4 MHz, N=5 MHz, and center 6 PRBs are not used. Referring toFIG. 12, K=3 and legacy UEs may be assigned to some PRBs. The remainingPRBs are assigned for 3 subDLBWs with consideration of alignment of RBS.

If N=10 MHz, the more cases may be possible.

For another approach, the subband may be created from the edge where asmall size of narrowband may be formed in the center. A DL narrowbandmay consist of a set of contiguous PRBs. In case that a low cost UEneeds to monitor PSS/SSS/PBCH of a cell, it may be retuned to center 72subcarriers (excluding system DC) if a low cost UE can support at least1.4 MHz RF bandwidth and baseband processing. If not, it may be retunedto a dedicated narrowband where synchronization and/or MIB istransmitted. A DL narrowband whose center frequency is aligned withcenter frequency of system bandwidth may be fully overlapped with center72 subcarriers (excluding system DC). This narrowband may be calledcenter narrowband. Other than the center narrowband, multiplenon-overlapped DL narrowbands may be specified for system bandwidthwider than 3 MHz. The number of DL narrowbands may be 1 in 1.4 MHz, 3 in3 MHz, 5 in 5 MHz, 9 in 10 MHz, and 17 in 20 MHz. For the narrowbandsnot adjacent with center narrowband, the size of narrowband may be 6PRBs. A UL narrowband may consist of a set of contiguous 72 subcarriers.For a UL narrowband, non-overlapped narrowbands may be specified forsystem bandwidth wider that 3 MHz. The size of each narrowband may be 6PRBs.

FIG. 13 shows an example of a center narrowband according to anembodiment of the present invention. Referring to FIG. 13, when thesystem bandwidth is 3 MHz, the center narrowband, which is the regionwhere data/control signal can be scheduled or not, consists of center 3PRBs. A UE may monitor center 72 subcarriers (6 PRBs) for PSS/SSS/PBCH.

FIG. 14 shows another example of a center narrowband according to anembodiment of the present invention. Referring to FIG. 13, when thesystem bandwidth is 5 MHz, the center narrowband, which is the regionwhere data/control signal can be scheduled or not, consists of center 1PRB. A UE may monitor center 72 subcarriers (6 PRBs) for PSS/SSS/PBCH.

FIG. 15 shows another example of a center narrowband according to anembodiment of the present invention. Referring to FIG. 13, when thesystem bandwidth is 10 MHz, the center narrowband, which is the regionwhere data/control signal can be scheduled or not, consists of center 2PRBs. A UE may monitor center 72 subcarriers (6 PRBs) for PSS/SSS/PBCH.

To allow efficient operation, in case of hopping is used, the mapping of6 PRBs to a center narrowband lower than 6 PRBs may be as follows.

(1) The first PRB in the center narrowband may be mapped to the firstPRB (and so on). In this case, some PRBs in 6 PRBs cannot be mapped tothe center narrowband lower than 6 PRBs which will be rate matched.

(2) Center of the center narrowband may be mapped to the center ofcenter PRBs such that PRBs in the edge may not be used or mapped in thecenter narrowband. For example, in case of 4 PRBs, two PRBs in the edgemay not be mapped.

(3) A UE may assume that the center narrowband may not be used forfrequency hopping or data scheduling.

Rules for utilizing a subDLBW according to an embodiment of the presentinvention is described. Overall, at least one of the following rules maybe considered.

(1) If subDLBW other than a subDLBW in the center of a system bandwidthis used, DC subcarrier may be created by not transmitting or puncturingthe data in REs used for DC. To support legacy PDCCH transmission, REsnot used for PDCCH may be only punctured. Alternatively, REs in PDCCHregion may also be punctured (which may impact the legacy UE PDCCHreception performance which will be handled by the network by properadjustment of code rate or other means). Even though the PDCCH regionmay be punctured for DC subcarrier creation, it may be assumed that theRB boundary is not changed in the PDCCH region. In other words, RBallocation (for example, 12 subcarriers per RB other than RB containingDC subcarrier for a legacy UE) for a legacy UE may be assumed in thePDCCH region. For the PDCCH region, for multicast broadcast singlefrequency network (MBSFN), the first two OFDM symbols may be assumed asPDCCH region. For normal subframes, by higher layer configured, thenumber of first few OFDM symbols may be assumed as PDCCH region.

(2) If MBSFN subframe is used for creating more than one subDLBW for alow cost UE and the UE may read other subDLBW than the center only inMBSFN subframes, no consideration to handle cell-specific referencesignal (CRS) Vshift may be necessary. If not, subDLBW DC subcarrier maybe created in consideration of CRS RE location. However, to allow lowcomplex UE implementation, even with MBSFN subframe, it is desirable notto change Vshift value of CRS mapping. In other words, CRS RE mappingpattern needs to be maintained as fixed regardless of the location ofsubDLBW. If the subDLBW outside of the center subDLBW is accessed innormal subframe as well, consideration on CRS RE location may be needed.More importantly, CRS RE may not be used for DC subcarriers.

(3) To maximize the spectral efficiency or minimize the unused PRBs,alignment of subDLBW to RBG may be considerable. When it create asubDLBW which requires 6 PRBs+1 subcarrier for a DC subcarrier (and thusrequires 7 PRBs), it should maximize the usable RBGs which is determinedbased on system bandwidth.

(4) CRS transmission for PDCCH region or region may be accessed by alegacy UE regardless of MBSFN subframe or normal subframe followinglegacy CRS RE mapping.

(5) CRS transmission for non-PDCCH region in MBSFN subframe may follow1.4 MHz system bandwidth CRS transmission centered at the DC subcarrierof a subDLBW in terms of RE mapping and sequence generation.Alternatively, CRS transmission in non-PDCCH region in normal and/orMBSFN subframe may still follow system bandwidth. In which case, the UEneeds to read CRS a bit differently depending on where the subDLBW islocated. If the subDLBW is in center 6 PRBs, CRS mapping is same as 1.4MHz system bandwidth system. However, if subDLBW is not in center 6PRBs, the RE mapping of CRS may follow system bandwidth which isdifferent from RE mapping of 1.4 MHz system bandwidth.

(6) If a subband overlaps partially with center 6 PRBs where the centerof a subband is different from the center of system bandwidth, it is upto UE implementation to handle possibly two DC subcarriers. To avoidthis case, it may be assumed that a subband may not be overlapped withcenter 6 PRBs partially. If it is overlapped, either it may be totallyoverlapped or only 5 PRBs out of the center 6 PRBs (in case odd systembandwidth) may be used for a subband. In other words, if a subband ispartially overlapped with center 6 PRBs, the center frequency of thatsubband may be assumed as the center frequency of the system bandwidth.In that case, to align with legacy PRB boundary, in odd system bandwidthcases, only 5 PRBs may be used as a valid PRBs in that subband. Asubband size may be smaller than 6 PRBs. Similarly, if SIB istransmitted in center 6 PRBs, in odd system bandwidth, to align withlegacy PRB mapping, it may be assumed that only 5 PRBs carry SIB. Inother words, half-PRBs in the start and end may not be used for datatransmission in odd system bandwidth.

FIG. 16 shows an example of CRS RE mapping to subDLBW other than center6 PRBs according to an embodiment of the present invention. FIG. 16corresponds to a case that CRS RE mapping is different between PDCCHregion and MBSFN region. Referring to FIG. 16, if different CRS REmapping in PDCCH region and MBSFN region (i.e. non-PDCCH region) isused, a low cost UE may need to assume different CRS RE pattern in firsttwo OFDM symbols and the rest of OFDM symbols. Thus, in this case, it ismore desirable not to read first two OFDM symbols (or regions wherelegacy UE can access). If this approach is used, the actual subcarriercarrying the CRS in the first slot (e.g. first OFDM symbol) and thesecond slot change.

FIG. 17 shows another example of CRS RE mapping to subDLBW other thancenter 6 PRBs according to an embodiment of the present invention. FIG.17 corresponds to a case that CRS RE mapping is consistent regardless ofregion. Referring to FIG. 17, the same subcarrier is used regardless ofDC subcarrier. Then, a legacy UE may be able to read CRS even withcreating a set of subDLBWs. However, from a low cost UE perspective,depending on its subDLBW location and the location of DC subcarrier, CRSpattern (e.g. Vshift value) may change. Thus, depending on the accessingsubDLBW, it needs to adjust CRS pattern. For example, in FIG. 17, thebottom PRB may have Vshift=4, and the upper PRB may have Vshift=5. Thus,different Vshift or CRS pattern for lower PRBs than DC subcarrier orhigher PRBs than DC subcarrier (in terms of frequency) may be required.This only needs in case of introducing artificial DC subcarrier, thus,when a UE access the center 6 PRBs, this is not needed. Thus, twodifferent implementations may be needed and the UE may need to switchbetween both implementations per subframe.

Determining location of artificial DC subcarrier for a subDLBW(subcarrier index) according to an embodiment of the present inventionis described. To allow DC subcarrier not interfering CRS transmission,the location of DC subcarrier (REs punctured) may be configured by PBCHor SIB. Or, the location of DC subcarrier may be higher layer configuredfor each UE assigned to that subDLBW. Or, it may be computed based oncell ID or the RE mapping of CRS. For example, (subcarrier cell ID) %6+m (e.g. m=1) may be used for DC subcarrier in a RB. The motivation isto minimize the impact of DC subcarrier to support a low cost UE in asubDLBW which may not be in center (center frequency already provides DCsubcarrier, thus no additional handling is needed if subDLBW is thecenter 6 PRBs). Alternatively, DC subcarrier may not be created for asubband outside of center. In this case, the performance may bedegraded. Also, if DM-RS based data modulation is used, DM-RS RE may notbe used for the artificial DC subcarrier. Alternatively, centersubcarrier out of 6 PRBs may be used for DC subcarrier. Since there arepossibly two subcarriers belonging to the different PRBs, either one maybe used. If the subcarrier does not carry CRS, the lower frequencysubcarrier may be used for DC subcarrier. Otherwise, the higherfrequency subcarrier may be used for DC subcarrier.

SubDLBW or SubULBW determination for each channel according to anembodiment of the present invention is described. When a set of subDLBWand/or set of subULBW is defined, the location of frequency for eachchannel may be determined differently depending on the channel type. Interms of determining frequency location for each channel, followings maybe considered.

(1) PBCH: If legacy PBCH is used, it may be considered that legacy PBCHis transmitted over the center 6 PRBs. For repeated PBCH to supportcoverage enhancements, the repeated PBCH may be located in center 6PRBs. Alternatively, Assuming that coverage enhancement is supported bythe network with more than 1.4 MHz system bandwidth, the repeated PBCHmay be placed in a different but prefixed location. If new PBCH isconsidered, it may be considered that new PBCH is transmitted in adedicated location based on the assumption that the network has morethan 1.4 MHz system bandwidth such that the dedicated subband may not beplaced in the center 6 PRBs. By default, the location may be the center6 PRBs as well. The location and RE mapping for the new PBCH, however,may not be changed based on the overall system bandwidth. The design maybe consistent regardless of actual system bandwidth.

(2) SIB: If new SIB is considered, fixed location may be used for SIBtransmission. To allow efficient use of resources, the location of SIBmay be prefixed which may be prefixed per system bandwidth inconsideration of alignment with PRG and/or RBG. For example, in systembandwidth of 100 PRBs system, since RBG size is every 2 PRBs, and if thenumber of PRBs used for SIB is for example 4, 4 PRBs may bepredetermined which is aligned with PRG/RBG. To align with PRG, two PRGsmay be allocated near center or in some frequency location may beprefixed for SIB location. In other words, a default location of SIB maybe different per system bandwidth. Furthermore, the location of SIB maybe changed over subframes. The location may be predetermined dependenton system frame number (SFN) or subframe index or may change/hop basedon a cell-specific pattern. Furthermore, the location of SIB may bedifferent based on cell ID. It may be determined based on both cell IDand system bandwidth. Per system bandwidth, there may be multiplePRG/RBGs where SIB may be located and the location may be selected basedon cell ID. To support this, a UE may need to acquire system bandwidthbefore reading SIB. Furthermore, the location of SIB1 and SIB2 may bedifferent and other SIBs may be transmitted in different locations. Ifneeded, the location of other SIBs may be signaled from either SIB1 orSIB2. Also, the number of repetitions/periodicity of SIBs may besignaled from SIB1 or SIB2.

(3) Paging: Considering particularly coverage enhancements, the locationof paging may not be desirable if it is fixed in center 6 PRBs. A UE mayreceive paging once it is at least camped on a cell, thus, the UE may beable to know the system bandwidth of the cell. The location of pagingmay be determined based on at least one of cell ID, P-RNTI, UE ID,subframe index (paging subframe), or radio frame index (paging radioframe). Also, a combination of those parameters may be used to determinethe location of paging occurrence from the frequency and/or timeresource perspective. For repeated paging, the location may be changedor fixed. A fixed location in center 6 PRBs may also be considered.

(4) RAR: The location of RAR may be determined based on at least one ofpreamble index used for PRACH, cell ID, RA-RNTI, higher layerconfiguration (such as via SIB), subframe index (RAR starting subframe),or radio frame index (RAR starting radio frame). A combination of thoseparameters may be used to determine the location of RAR occurrence fromthe frequency and/or time resource perspective. For repeated RAR, thelocation may be changed or fixed. A fixed location in center 6 PRBs mayalso be considered.

(5) PRACH: The location of PRACH may be determined based on at least oneof preamble index, UE ID, cell ID, subframe index (PRACH startingsubframe), or radio frame index (PRACH starting radio frame). Acombination of those parameters may be used to determine the location ofPRACH. A fixed location in center 6 PRBs may also be considered.

(6) Message 3: The location of message 3 may be determined based on RARdynamically (i.e. frequency location used for RAR may determine thefrequency or subULBW of message 3) or fixed or determined by RAR(explicitly indicated in RAR).

(7) EPDCCH CSS: The location of EPDCCH at CSS may be fixed in center.Alternatively, the location of EPDCCH at CSS may be fixed based on cellID. Alternatively, the location of EPDCCH at CSS may be fixed based onSI-RNTI or some RNTI. Location may change per subframe based on apattern.

(8) EPDCCH USS: The location of EPDCCH at CSS may be fixed or determinedbased on a pattern dynamically or semi-statically. The location ofEPDCCH at CSS may be determined based on at least one of UE ID, C-RNTI,cell ID, subframe index (EPDCCH starting subframe index), or radio frameindex (EPDCCH starting radio frame index). A combination of thoseparameters may be used to determine the location of EPDCCH at CSS.

(9) PUCCH: The location of PUCCH may be fixed or determined based on apattern dynamically or semi-statically. That is, the location of PUCCHmay be determined similar to EPDCCH or may mapped to the CCE of thefirst PDSCH where ACK/NACK is transmitted. For CSI feedback, a fixed(higher layer configured) location may be used.

(10) PDSCH: The location of PDSCH may be fixed or may be determineddynamically via DCI or semi-statically via higher layer.

(11) PUSCH: The location of PUSCH may be fixed or may be determineddynamically via DCI or semi-statically via higher layer.

Relationship between UE-specific subDLBW and cell-specific subDLBWaccording to an embodiment of the present invention is described. It maybe generally assumed that subDLBW configured for cell-specific channelsuch as SIB is different from UE-specific subDLBW. In that case, since aUE can access only one subDLBW in a subframe, if different location isused, frequency switch between UE-specific subDLBW and cell-specificsubDLBW may be necessary. To allow frequency switching delay, onesubframe or a few OFDM symbols before and after cell-specific subframewhere a UE monitors cell-specific subDLBW may be considered. Since a UEmay not access cell-specific channel all the time, a UE may autonomouslycreate a gap (frequency switching gap) by not receiving some data beforeand after cell-specific channel. Particularly, in a coverage enhancementmode, cell-specific channel may come in during the repetition of unicastdata. In such a case, the following approaches may be considered.

(1) A set of subframes which may carry cell-specific channel may beprefixed such that a UE can assume that any unicast data is not repeatedin a subframe where possibly cell-specific channel can be transmitted.In such a case, a gap for frequency switching before and aftercell-broadcast subframe may also be assumed that any repetition is notoccurred in those gaps either.

(2) A set of subframes where unicast channel may be transmitted may beused either for cell-specific or frequency switching or other purpose.

(3) Regardless of cell-specific channel, repetition may occur based onthe configuration. If a UE needs to read cell-specific channel (repeatedbroadcast), it may autonomously create gap and may not receive therepeated unicast channel in that subframe where cell-specific channel isbeing received.

(4) During the repetition of unicast channel, cell-specific channel maynot be received. Cell-specific channel may be received only when thereis no unicast data is being transmitted/received.

Here, unicast data may refer PDSCH transmission as well as (E)PDCCHtransmission for unicast data scheduling. Also cell-specific channel mayrefer PDSCH transmission as well as (E)PDCCH transmission forcell-specific data scheduling. In other words, even control channel anddata between unicast and broadcast may follow the option(s) addressedabove. Particularly, the last option means that control channel and datachannel between CSS and USS may not be occurred simultaneously within abundle. A new bundle of either control signal or data channel may startonly after the current bundle finishes.

SubDLBW/SubULBW determination in retransmission according to anembodiment of the present invention is described. Depending on thenumber of repetitions (or coverage enhancement level) required for eachtransmission, the number of subframes required for one bundledtransmission may be different. With many UEs with different repetitionor coverage enhancement levels, it may be difficult to manage differentnumbers of subframes in a subDLBW. Thus, one approach to consider is tomap subDLBW to coverage enhancement level or repetition level, such thatthe number of subframes used in a subDLBW is fixed where differentsubDLBWs may have different number of repetitions/coverage enhancementlevels. When a UE is configured by higher layer with coverageenhancement level or repetition level, it may refer subDLBW associatedwith the configured coverage enhancement/repetition level.Alternatively, by configuring a subDLBW, a UE may also infer coverageenhancement/repetition level. Or, it may also configure subDLBW andcoverage enhancement/repetition level as well.

When a UE performs retransmission, since initial transmission alreadytransmits a bunch of PUSCH, it is desirable to reduce the number ofrepetitions. In such a case, one approach is to switch to differentsubDLBW with smaller repetition level or lower coverage enhancementlevel for each repetition. The larger retransmission counter, thesmaller coverage enhancement/repetition level may be considered. Interms of resource allocation, the same resource allocation per initialtransmission UL grant may be used unless another DCI is received toindicate otherwise.

RAR retransmission (repetition number change) according to an embodimentof the present invention is described. Due to miscomputation of coverageenhancement/repetition level, the RAR reception may fail. In that case,if the network receives PRACH retransmission, it may increase the RARrepetition level. One simple approach is to map the repetition level ofRAR to PRACH repetition level such that RAR repetition level increaseswith PRACH retransmission. Another approach is to increase RARrepetition level per PRACH retransmission once the network detects theretransmission of PRACH from the same UE.

Paging retransmission (repetition number change) according to anembodiment of the present invention is described. Since a UE's coverageenhancement level may change, determining coverage enhancement level forpaging may be tricky. Thus, maximum coverage enhancement level forpaging may be considered. However, this may degrade system spectralefficiency particularly if the network does not have many UEs requiringlarge coverage enhancement level. Furthermore, if a UE's coverageenhancement level becomes larger than the maximum coverage enhancementlevel that the network can support, the network still may support largernumber of repetitions or the network may support larger coverageenhancement level for paging compared to other channels (i.e. maxcoverage enhancement level for paging may be larger than max coverageenhancement level for other channels). In terms of coverage enhancementlevel expectation from a UE perspective, the following options may beconsidered.

(1) Paging may always start from the lowest coverage enhancement level(i.e. coverage enhancement level=0 dB) and may move to the next coverageenhancement level if the initial paging fails. In this case, todetermine whether the initial paging has failed or not, it may beassumed that control channel scheduling the paging may be transmittedusing the maximum coverage enhancement level such that with highprobability, the UE can acquire the control channel at least. If theinitial transmission fails, the UE may assume that the larger coverageenhancement/repetition level is used for retransmission such that a UEmonitors the next or larger coverage enhancement/repetition level pagingoccasion/subframes.

(2) Paging may start from the coverage enhancement level which has beensuccessful last time (for the retransmission, higher repetition levelmay be used). For this, a UE/the camp-on cell may maintain the coverageenhancement level used in the last time.

(3) Paging may start from the coverage enhancement level which was usedin RRC_CONNECTED mode (for the retransmission, higher repetition levelmay be used). For this, a UE/the camp-on cell may maintain the coverageenhancement level configured in RRC_CONNECTED mode. Even with option, ifcoverage enhancement level changes, the last used coverage enhancementlevel may override the stored coverage enhancement level used inRRC_CONNECTED mode.

(4) Another option is to transmit signal coverage enhancement levelbefore transmitting paging using the maximum coverage enhancement levelin a preconfigured resource where the UE can interpret the resourceand/or coverage enhancement level of paging transmission if there is apaging. For this, a small transmission such as control channel basedtransmission to indicate the existence of paging with coverageenhancement level may be considered.

A signal generation for a subDLBW according to an embodiment of thepresent invention is described. Starting DC subcarrier as 0, subcarrierindex may start as if the system bandwidth is 1.4 MHz and the UE isserved in that 1.4 MHz system bandwidth. In other words, the signal maybe generated as follows where the number of PRBs is 6 and the number ofsubcarriers per RB is 12. This may be applied to signals transmitted innon-PDCCH region or OFDM symbols signaled by the network which may beused for a low cost UE. For example, if the higher layer signals that alow cost UE can access OFDM symbols 4-13, the signals transmitted inOFDM symbols 4-13 of a subDLBW used by a low cost UE based on 73subcarrier bandwidth (72 subcarriers+1 DC subcarrier) may followEquation 3 below.

$\begin{matrix}{{s_{l}^{(p)}(t)} = {{\sum\limits_{k = {- {\lfloor{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rfloor}}}^{- 1}{a_{k^{( - )},l}^{(p)} \cdot e^{j\; 2\pi\; k\;\Delta\;{f{({t - {N_{{CP},l}T_{s}}})}}}}} + {\sum\limits_{k = 1}^{\lceil{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rceil}{a_{k^{( + )},l}^{(p)} \cdot e^{j\; 2\pi\; k\;\Delta\;{f{({t - {N_{{CP},l}T_{s}}})}}}}}}} & {< {{Equation}\mspace{14mu} 3} >}\end{matrix}$

At least for PDSCH and/or DM-RS, signal generation described in Equation3 may be used. Further, when a subDLBW is used, the sequence generationof cell-specific signals/data, e.g. CRS, CSI-RS, may be assumed based onsystem bandwidth. Cell-specific data may be read in a set of PRBs for areduced bandwidth UE based on partial PRB reading out of wideband systembandwidth.

Consideration of impacts and multiplexing on legacy UEs according to anembodiment of the present invention is described. So far, it is assumedthat size of a subDLBW is 6 PRBs+1 DC (72 subcarriers+1 DC subcarrier=73subcarriers). However, subDLBW of 6 PRBs where 1 DC subcarrier iscreated by RE puncturing may also be considered. In this case, theavailable RE in a RB containing DC subcarrier may be smaller than otherRBs. However, this may be compensated by the network scheduling.

Even if this is used, DC subcarrier may be selected such that it doesnot collide with CRS transmission. One example as mentioned before is touse (Cell ID) % 6+1. Also, other mechanisms mentioned above may beapplicable as well. Even with 6 PRBs for 1.4 MHz without additional DCsubcarrier, in terms of transmission bandwidth, system bandwidth may beassumed to be 1.4 MHz from the RF and baseband processing perspective.One additional subcarrier (not carrying data for the low cost UE)processed in baseband may be treated as if REs containing no data. Ifthere is CRS transmission in that subcarrier, CRS may be read. In thiscase, however, signal generation may not consider the center DCsubcarrier. Only puncturing to minimize the interference may be used inREs for DC subcarrier.

Which area to read by a reduced bandwidth UE according to an embodimentof the present invention is described. A low cost UE may skip readingfirst few OFDM symbols as it does not give any useful information to theUE. The starting OFDM symbol where narrow band transmission occurs maybe signaled to a UE via PBCH, SIB or higher layer signaling. SIB1 maycarry the starting OFDM symbol for control/data channels. If a UE isconfigured by higher layer to apply different starting OFDM symbol thanit from SIB1, it may follow higher layer signaling rather than SIBsignaling. It may be only applicable to unicast transmission, whereasthe starting symbol may be determined by SIB and the starting symbol maybe by default determined by SIB and may be updated by dynamic orsemi-static signaling. In case of dynamic signaling, common DCI such asDCI format 1C may be utilized. It may be delivered periodically oraperiodically.

Also, if a UE knows the MBSFN configuration or a set of subframes whichmay not be used for legacy UEs, a different OFDM symbol startingposition from other normal subframes may be assumed. A separatesignaling to indicate control format indicator (CFI) value on thosesubframes may be further considered. Alternatively, a UE may performdecoding blindly two or more candidates of starting OFDM symbol suchthat the network may change the starting OFDM symbol dynamically.Another approach is to signal by scheduling DCI where unless indicatedotherwise, CFI value may be determined by the most recently receivedcontrol channel/DCI for unicast data transmission.

However, CRS transmission in the first few OFDM symbols still may beused for channel estimation and time/frequency tracking. Thus, for softbuffer to store law data, only OFDM symbols which can carry data/controlfor a low cost UE may be considered to further reduce the cost. However,there may be no legacy PDCCH in a TTI as the network may not transmitany PDCCH. This means that, in some cases, PDSCH for a reduced bandwidthUE may start from the OFDM symbol 0. Thus, from the bufferingperspective, it is yet desirable to consider buffering the entire OFDMsymbols (i.e. from 0 to 13 in normal CP and from 0 to 11 in extendedCP).

Furthermore, if MBSFN subframes are used for supporting low cost UEs,the used CP may be different from subframe #0 where the used CP may besignaled via PBCH, SIB or higher layer. If MTC-PSS/MTC-SSS is used, theCP may be estimated/detected by reading MTC-PSS/MTC-SSS. Or for a lowcost UE, it may be assumed that extended CP is always used.

Assumption regarding which subframes to read by a reduced bandwidth UEaccording to an embodiment of the present invention is described.Overall, it is more natural to assume that if subDLBWs (if more than 1is used) other than center 6 PRBs are used for low cost UEs, it may berestricted to MBSFN subframe. In other words, a low cost UE may readdifferent subDLBWs other than center 6 PRBs only in MBSFN subframe, andread center 6 PRBs in non-MBSFN subframes. Thus, a reduced bandwidth UEmay assume that there are a set of subframes readable by itself (i.e.not every subframe is available for a low cost UE). If a low cost UEreads both MBSFN and non-MBSFN subframes, the CP length may bedetermined by CP used in normal DL subframe. It is not assumed that alow cost UE assumes different CP length per subframe.

In general, a low cost UE may be configured with a set of subframes anda set of subDLBWs to read at each subframe or per subframe, which may behigher layer configured. The same principle may be applied to theboundary of RB and/or CRS RE mapping. For example, if RB boundary and/orCRS pattern for a low cost UE is different, which requires CRStransmission pattern change to allow simple UE implementation, this maybe only applied in MBSFN subframes. Thus, if a low cost UE needs to readonly MBSFN subframes, different RB allocation or CRS RE mapping based onartificial DC subcarrier (artificially created DC subcarrier for asubDLBW by puncturing by the network) may be used. If the UE needs toread both normal and MBSFN subframe, CRS mapping for a subDLBW mayfollow the pattern assuming RB allocation with no DC subcarrier. Inother words, by creating artificial DC subcarrier in normal subframe, 3PRBs in the lower side of DC subcarrier (or higher side of DC subcarrierin terms of frequency) may have one subcarrier shifted CRS patterncompared to the rest of 3 PRBs. Furthermore, depending on the locationof DC subcarrier, the CRS pattern may change.

FIG. 18 shows an example of Vshift for CRS depending on a DC subcarrieraccording to an embodiment of the present invention. FIG. 18 correspondsto a case that CRS RE mapping is different between PDCCH region andMBSFN region.

FIG. 19 shows another example of Vshift for CRS depending on a DCsubcarrier according to an embodiment of the present invention. FIG. 19corresponds to a case that CRS RE mapping is consistent regardless ofregion. If the same CRS pattern is assumed regardless of artificial DCsubcarrier, the CRS RE mapping may change based on the location of DCsubcarrier. Referring to FIG. 19, if Vshift value is 4 in the systembandwidth with PCID, if DC subcarrier is created at subcarrier 5 (whichis 4+1), if the same RE mapping is used, Vshift value for the CRSpattern in the lower frequency part from the DC subcarrier is Vshift=2and higher frequency part from the DC subcarrier is Vshift=5. Thus, theUE needs to compute Vshift (or CRS pattern) based on the location of DCand the PCID. If DC subcarrier is used at subcarrier of Vshift+1, Vshiftvalue for CRS pattern for a RB for a low cost UE may become 5. Thus, aUE may be hard-coded about Vshift value.

However, if DC subcarrier is created based on Vshift, among cells, thelocation of subDLBW may not be aligned. In this case, inter-cellinterference issue may become considerable. Thus, it may be considerableto fix the location of DC subcarrier (such as subcarrier 6th of a centerRB of a subDLBW regardless of Vshift). In this case, if CRS RE maypresent in that DC subcarrier, it may not be able to be punctured. Thus,the cell may not create any subDLBW in that case other than center 6PRBs or the cell may allow only MBSFN subframe usable for subDLBW (inwhich case, CRS in PDCCH region may not be punctured). In terms ofimplementation, since CRS based channel estimation is a bit separatelogic from data decoding, it is also possible to assume the same CRS REmapping regardless of region, where CRS pattern is always determinedbased on system bandwidth rather than a location of subDLBW.

It may be further assumed that a low cost UE may not need to supportpositioning reference signal (PRS) and/or CSI-RS based CSI feedbacks.

Regardless of which mechanism is used, a low cost UE may need to knowthe system bandwidth to determine RE mapping. Thus, MTC-PBCH maytransmit either system bandwidth of the network or whether systembandwidth is odd or even (i.e. the number of PRBs for the systembandwidth is odd or even, for example, for 3 MHz system, the network maysignal odd).

If K is more than 1, the UE may need to know the system bandwidth toread CRS and necessary signals which is scrambled based on the DL systembandwidth.

Based on the above discussions, in terms of CRS reading, the followingoptions may also be considerable.

(1) Considering fixed subDLBW used for a low cost UE, CRS in center 6PRBs may be read by a low cost UE.

(2) Considering potentially different subDLBW from a center 6 PRBs, CRSmay read by a low cost UE which are transmitted only in non-PDCCHregion. In this case, the number of CRS REs may be reduced and thuschannel estimation, time/frequency tracking may be reduced. Thus,increase of CRS RE density may be considered. However, this does notrequire different UE implementation regardless of subDLBW location(whether in center 6 PRBs or not). If only MBSFN subframe is readable bya UE, CRS RE pattern of extended CP at least for normal CP framestructure may be used. Since there are 12 OFDM symbols, the pattern ofextended CP may be used for non-PDCCH region in MBSFN subframe.

(3) Considering potentially different subDLBW from a center 6 PRBs,depending on the location of a subDLBW that a low cost UE reads,different RE mapping of CRS may be assumed (if it is center 6 PRBs, CRSRE mapping does not account for center DC subcarrier, whereas if thesubDLBW is not in center 6 PRBs, CRS RE mapping is regardless of REs forDC subcarrier), and thus, it may require different logic of CRS readingdepending on the location.

(4) CRS RE mapping pattern may always be determined based on systembandwidth regardless of location of subDLBW (which is somewhatequivalent to (3)).

Given that PDCCH is not shared between legacy UE and low cost UE, it isdesirable to support option (2) described above to minimize UEcomplexity. However, this requires 6 PRBs+1 subcarrier for a subDLBWsize. If a subDLBW size is 6 PRBs only, option (3) may be necessary.Similarly for other RS such as DM-RS, CSI-RS, depending on the size of asubDLBW not in center 6 PRBs, the RE mapping for each RS may bedifferent. If 6 PRBs is used for a subDLBW, signal generation may followEquation 4 below.

$\begin{matrix}{{s_{l}^{(p)}(t)} = {{\sum\limits_{k = {- {\lfloor{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rfloor}}}^{- 1}{a_{k^{( - )},l}^{(p)} \cdot e^{j\; 2\pi\; k\;\Delta\;{f{({t - {N_{{CP},l}T_{s}}})}}}}} + {\sum\limits_{k = 1}^{{\lceil{N_{RB}^{DL}{N_{sc}^{RB}/2}}\rceil} - 1}{a_{k^{( + )},l}^{(p)} \cdot e^{j\; 2\pi\; k\;\Delta\;{f{({t - {N_{{CP},l}T_{s}}})}}}}}}} & {< {{Equation}\mspace{14mu} 4} >}\end{matrix}$

In Equation 4, it is assumed that that REs used for DC subcarrier residein the center (between two subcarriers of the center, the higherfrequency subcarrier is used), and the number of PRBs is 6 and thenumber of subcarrier per PRB is 12. Or, a low cost UE may read onlyportion of data based on the assumption that signal is generated basedon the system bandwidth. In that case, the number of PRBs may be thesame as the system bandwidth. In this case, a UE may assume that REsused for DC subcarrier are punctured.

RB allocation for a reduced bandwidth UE according to an embodiment ofthe present invention is described. Considering potentially different RBallocation for a low cost UE, various kinds of options for datatransmission/RB allocation may be considered.

FIG. 20 shows an example of a RB allocation with artificial DCsubcarrier according to an embodiment of the present invention. FIG. 20shows a case that the size of subDLBW is 6 PRBs. In this case, the RBallocation by artificial DC subcarrier may be aligned with legacy PRB.

FIG. 21 shows another example of a RB allocation with artificial DCsubcarrier according to an embodiment of the present invention. FIG. 21shows a case that the size of subDLBW is 6 PRBs+1 subcarrier. In thiscase, the RB allocation by artificial DC subcarrier may be separate fora reduced bandwidth UE from legacy PRB.

RB allocation issue for a center subDLBW depending on system bandwidthaccording to an embodiment of the present invention is described. If aUE supports only 1.4 MHz, depending on the system bandwidth (even orodd), the RB mapping of center 1.4 MHz subDLBW may be different aroundthe center DC subcarrier. If the system bandwidth is even, DC subcarrieris located between two PRBs, whereas if the system bandwidth is odd, DCsubcarrier is located within a PRB. Thus, the transmission bandwidth maynot seem to be aligned if odd system bandwidth supports 1.4 MHz. Thereare potentially different approaches to address this issue.

(1) Only even system bandwidth may support center 1.4 MHz subDLBW for alow cost UE.

(2) A virtual RB based on 1.4 MHz may be reformed. If this is used, CRStransmission within a PDCCH region may not be readable or decodable by alow cost UE. Or, only 6 subcarriers may shifted. In other words, RBmapping may change, yet, the same CRS location may be used at least forcenter 1.4 MHz. (CRS sequence is okay with shifting RB 6 subcarriers asthe starting point from DC is remained as the same).

FIG. 22 shows another example of a RB allocation with artificial DCsubcarrier according to an embodiment of the present invention.Referring to FIG. 22, only 6 subcarriers are shifted for a RB allocationfor low cost UE.

(3) This RB allocation difference may occur only for odd systembandwidth case. Since legacy UE and low cost UE may not share the PDCCH,this new allocation for a low cost UE may be acceptable. However, thismay cause that more RBs are not schedulable to a legacy UE, as it maynot be aligned with RB allocation of low cost UE. For example, side twoPRBs (where half PRB is used for center 6 PRBs for 1.4 MHz) may not beusable to schedule a legacy UE.

If subDLBW is created in other location(s) other than the center 1.4MHz, RB allocation of a low cost UE and RB allocation for a legacy UE,which coexists within a system bandwidth, may be different. Necessarygap of subcarriers to align different allocations may be left up tonetwork implementation. From a UE perspective, if 73 carriers areassumed as a subDLBW size, RB allocation may be [12 subcarriers][12subcarriers][12 subcarriers][DC][12 subcarriers][12 subcarriers][12subcarriers]. If 72 carriers are assumed as a subDLBW size, RBallocation may be either [12 subcarriers][12 subcarriers][11subcarriers][DC][12 subcarriers][12 subcarriers][12 subcarriers] or [12subcarriers][12 subcarriers][12 subcarriers][DC][11 subcarriers][12subcarriers][12 subcarriers]. Either approach may have the impact onDM-RS. For example, the second approach is used, DM-RS pattern forantenna ports 7 or 8 may not be able to utilize 4 REs of the 4th PRB asthe first subcarrier is punctured. If the first approach is used, DM-RSpattern for antenna ports 9 or 10 may not be able to utilize 4 REs of3rd PRB as the last subcarrier is punctured.

Another approach to consider is to read more than 1.4 MHz or more than1.08 MHz for 6 PRBs operation by allowing a wider-band RF capability(1.4 MHz+12 subcarrier (180 KHz)=˜1.6 MHz) where baseband can onlyprocess 6 PRBs. By reading more PRBs at least for odd system bandwidth,either the lower side of 6 PRBs or the higher side of 6 PRBs may be usedfor data reception (similarly, this may be applied to UL transmission aswell).

FIG. 23 shows another example of a RB allocation with artificial DCsubcarrier according to an embodiment of the present invention.Referring to FIG. 23, a wideband is read by RF, and the lower side of 6PRBs are used for data reception.

FIG. 24 shows another example of a RB allocation with artificial DCsubcarrier according to an embodiment of the present invention.Referring to FIG. 24, a wideband is read by RF, and the higher side of 6PRBs are used for data reception.

The network may signal whether to use the lower side or the higher sideof 6 PRBs via PBCH or it may be predetermined. This approach has adrawback that a reduced bandwidth requires to read 7 PRBs, however, thiswill allow the alignment of PRBs between legacy and low cost UEs. Interms of signal generation, however, the UE may need to interpret thisbased on system bandwidth. For other subband (not in the center), asimilar mechanism may be utilized. This may require reading of systembandwidth via PBCH or other means (e.g. a new PBCH for low cost UE). Ifincrease of RF bandwidth becomes an issue, a UE may read the determined6 PRBs by skewing the location of DC subcarrier. Or, a UE may use lessfiltering gap. In other words, the gap between channel bandwidth andtransmission bandwidth may become smaller (which however may increasethe UE cost).

FIG. 25 shows an example of relationship between channel bandwidth andtransmission bandwidth. Referring to FIG. 25, channel bandwidth isconfigured, and within the channel bandwidth, transmission bandwidth isconfigured. According to an embodiment of the present invention, the gapbetween the channel bandwidth and the transmission bandwidth may becomesmaller.

More generally, to align a subDLBW for a bandwidth reduced UE with PRGand/or RBG, it may be expected that a UE supporting reduced bandwidthreads more than 1.4 MHz from RF perspective. For example, with 100 PRBssystem, since RBG size is 4 PRBs, a UE may read up to 12 PRBs (and usethe first two RBGs or the last two RBGs), then the waste may be reducedfrom 6 PRBs to 2 PRBs assuming that a legacy UE cannot be scheduled onpartial RBG if a low cost UE in the RBG is scheduled. This problembecomes more severe with PRG since a UE will be scheduled in a PRG unit.For example, with 50 PRBs system bandwidth, PRG size is 3 PRBs. In thatcase, by reading up to 10 PRBs, a UE may save 3 PRBs waste if onlycenter 6 PRBs are used then 3 PRBs may not be scheduled for DM-RS.

General RB allocation issue for a low cost UE according to an embodimentof the present invention is described. So far, it was assumed that a lowcost UE reads 6 PRBs as either [3 PRBs][DC subcarrier][3 PRBs] or [35subcarriers][DC subcarrier][36 subcarriers] or [36 subcarriers][DCsubcarrier][35 subcarriers]. However, an option to align RB boundarybetween legacy UE and low cost UE may also be considered. In this case,a low cost UE may read [x subcarriers][12 subcarriers][12 subcarriers][ysubcarriers][DC subcarrier][12-y-1 subcarriers][12 subcarriers][12subcarriers][12-x subcarriers] where x and y may be in between [0-12].

In terms of resource allocation, which is assumed to be 6 PRBs, [xsubcarriers]+[12-x subcarriers] may form one virtual RB for a low costUE. For the convenience, a segment index from 0 to 7 may be set where 0maps to [x subcarriers] and 7 maps to [12-x subcarriers] out of 72subcarriers used for a subDLBW other than a subDLBW in the center. Forthe subband in the center, the number of subcarriers may be 73.

For a resource allocation (physical resource allocation), the PRB indexmay start from segment 0 for 12 subcarriers. In case that 72 subcarriersare used for subDLBW, PRB index may start in every 12 subcarriers. If 73subcarriers are used, PRB allocation may be performed as if a low costUE is a legacy UE in that system bandwidth.

Thus, RE mapping, from a low cost UE perspective, may be based onphysical subcarrier index which is based on the system bandwidth.

This may not be work well with DM-RS based data transmission. If DM-RSbased transmission is used, the first and last segment may not be usedfor data scheduling. In other words, physically adjacent subcarriers maybe used as a MTC-PRB if DM-RS based transmission is used.

In this case, if the network wants to keep the same RB for resourceallocation, [x subcarriers], if x is not 0 or 12, and [12-x subcarriers]may not be used for any data/control scheduling (as only partial portionof subcarriers in a physical PRB is used for data/control transmissionfor a low cost UE).

Alternatively, the network may utilize those area to transmit some data,then the remaining [12-x subcarriers] and [x subcarriers] may not beusable for a legacy UE as only partial RB is available for a legacy UEif those are used for scheduling low cost UE. Even with that waste, ifthe network wants to maintain the same physical PRB allocation for thelegacy UE and low cost UE, it may utilize it. If any scheduling for alow cost UE is allowed in those fragmented PRBs, [x subcarriers] and[12-x subcarriers] may be treated as one PRB. In this case, unless x is12, it maps to the last PRB index (i.e. PRB index 5). In other words,PRB 0 (for a low cost UE) may start at the first segment.

FIG. 26 shows an example of fragmented segments according to anembodiment of the present invention. Referring to FIG. 26, if thosesegments are used, center 6 PRBs for a low cost UE may be utilized in anODD system bandwidth network. That is, 6 subcarriers before PRB index 0and 6 subcarriers after PRB index 6 may be treated as one PRB. In thiscase, any RS pattern may follow RS pattern based on PRB based on systembandwidth. Thus, RS pattern for a low cost UE, depending on x, maychange. For example, if x=6, DM-RS pattern for PRB index 5 may be thesame as one PRB. To handle this, a UE may need to know x, and the numberof subcarriers used in one subDLBW. When considering DC subcarrier, inaddition to avoidance on collision with CRS, avoidance with DM-RS mayalso be desired.

If this is used, from a low cost UE perspective, RB definition is rathervirtual than physical. The UE may need to map the signal mapping byderiving actual REs used for control signal/data scheduling by mappingbetween virtual RB (based on DC subcarrier location, the number ofsubcarriers used in a subDLBW) and physical RB based on systembandwidth. If this is used, the UE may need to be informed with systembandwidth.

Furthermore, this option may be used if a low cost UE needs to read bothnormal and MBSFN subframes. In normal subframe, it may be easier tofollow legacy UE PRB. To minimize the impact on UE implementation,subDLBW may also be aligned with PRBs, and in this case, DC subcarriermay be used either first or the last subcarrier of a PRB in the center.

In case of odd system bandwidth, since for center 6 PRBs, it is notpossible to align subDLBW to PRBs, a dedicated subDLBW (of 72subcarriers) may be used instead where MTC-PSS/MTC-SSS are used. In thiscase, a low cost UE may assume that subDLBW and PRBs based on systembandwidths are always aligned.

The above approach may be more desirable considering that some signals,such as CSI-RS, are shared between legacy UE and low cost UE. Ifdifferent RB allocation is used between low cost UEs and legacy UEs, thenetwork may configure proper CSI-RS configuration to a low cost UE suchthat it may be aligned between a legacy UE and low cost UE.

Alternatively, a MTC UE may be configured with a set of REs assumed tobe punctured (such as zero-power CSI-RS configuration) and it may notread CSI-RS.

While creating a DC subcarrier, the following additional considerationmay also be given. For example, the frequency difference between this DCsubcarrier for the subDLBW and the center frequency of the systembandwidth may be multiple of 100 KHz. Alternatively, if subband maycarry MTC-PSS/MTC-SSS, it is also desirable to use non-multiple of 100Khz for the raster of DC subcarrier.

Gap between subDLBW/subULBW according to an embodiment of the presentinvention is described. To allow flexible operation, it is alsoreasonable to consider a gap between subDLBWs (and also betweensubULBWs). The gap size may be changed depending on the location of DCsubcarrier and the alignment with PRB allocation for a legacy UE whichshares the system bandwidth with low cost UEs. For example, if DCsubcarrier is used in subcarrier #2 of PRB #4, only two subcarriers ofPRB #1 may be used. However, since the rest 10 subcarriers of PRB #1 maynot be schedulable to legacy UEs, the gap may be 10 subcarriers in thatcase. This flexible gap duration also allows flexible configuration ofDC subcarrier within a PRB. In general, up to one PRB may be used for agap between subDLBWs and/or subULBWs.

If PRBs of a low cost UE and legacy UE are not aligned, the transmissionof CSI-RS may become challenging. In this case, either a low cost UE mayconsider CSI-RS transmission based on legacy UE PRB allocation or mayconsider that CSI-RS transmission will not occur. Thus, CSI-RStransmission may be treated as interference to a low cost UE. Forzero-power CSI-RS, it is up to the network to adjust zero-power CSI-RSconfiguration aligned with PRBs. If a subDLBW may utilize 73 subcarriersoutside of center 6 PRBs, it is difficult to align zero-power CSI-RS.Thus in this case, a UE may assume that zero-power CSI-RS configurationapplies only for 72 subcarriers. Or, in this case, it may be assumedthat zero-power CSI-RS is not used for a low cost UE.

Considering RB allocation for a low cost UE, it may be desirable toalign subDLBW with PRB allocation for a legacy UE, and separate RBallocation for data scheduling and other cell-common RS/channeltransmission. For cell-common RS/channel, it may be expected that PRBallocation for a legacy UE is used for a reduced bandwidth UE. For datatransmission and scheduling, it may be assumed that 1.4 MHz based PRBallocation for a low cost UE is used. If EPDCCH is used, it may betreated as PDSCH. If PDCCH is used for a low cost UE, the same handlingto cell-common channel may be considered. For DM-RS, it may be treatedsimilar to PDSCH. Since PDCCH for a low cost UE is scheduled within aPDSCH region, for PDCCH, RB allocation may follow the rule for PDSCH.For UL, since multiplexing with other legacy UEs are important, PRBallocation for a legacy UE may be used at least for PUCCH/SRS. ForPRACH/PUSCH, either option may be considered. If PUCCH/SRS is limited toa subULBW, PUCCH/SRS may also follow 1.4 MHz PRB allocation.

FIG. 27 shows an example of a method for allocating resources to a lowcost UE according to an embodiment of the present invention.

In step S100, the BS allocates at least one sub-bandwidth among a systembandwidth to a low cost UE. The BS may further partition the systembandwidth into a plurality of sub-bandwidths. The at least onesub-bandwidth may include a set of resource PRBs that the low cost UEcan access at a given subframe. The at least one sub-bandwidth may belocated at center of the system bandwidth. The at least onesub-bandwidth may be determined based on a start offset and a number ofavailable sub-bandwidths. The at least one sub-bandwidth may beallocated from a lowest indexed PRBs or from a highest indexed PRBsamong available sub-bandwidths. The at least one sub-bandwidth may bealigned with a RBG. The at least one sub-bandwidth may be allocated fromPRBs in edge of the system bandwidth. The at least one sub-bandwidth maybe overlapped with a center narrowband. The BS may further transmit asynchronization signal via the allocated at least one sub-bandwidth. Asize of the one sub-bandwidth may be 72 subcarriers or 73 subcarriers.

In step S110, the BS transmits information on the allocated at least onesub-bandwidth to the low cost UE. The information on the allocated atleast one sub-bandwidth may be transmitted via PBCH for the low cost UE,SIB for the low cost UE, a higher layer, MAC CE or DCI. The informationon the allocated at least one sub-bandwidth may include an index of theallocated at least one sub-bandwidth. The information on the allocatedat least one sub-bandwidth may include a list of the allocated at leastone sub-bandwidth.

Further, description of the present invention described above may beapplied to the embodiment of FIG. 27.

FIG. 28 shows another example of a method for allocating resources to alow cost UE according to an embodiment of the present invention.

In step S200, the BS allocates resource blocks including a punctured DCsubcarrier to a low cost UE. The allocated resource blocks may not belocated at center of a set of resource blocks that the low cost UE canaccess at a given subframe. The given subframe may be a normal subframeor a MBSFN subframe. The puncture DC subcarrier may include REs not usedfor a PDCCH. A location of the punctured DC subcarrier may be configuredbased on location of REs used for a CRS. A location of the punctured DCsubcarrier may be configured based on a cell ID. A location of thepunctured DC subcarrier may be configured by a PBCH, a SIB, or a higherlayer signaling. A start symbol of the allocated resource blocks may beindicated via a PBCH, a SIB or a higher layer signaling. The allocatedresource blocks may be aligned to a RBG. A CRS RE mapping in theallocated resource blocks may be different or identical between a PDCCHregion and a MBSFN region in the allocated resource blocks. A number ofsubcarriers in the resource blocks including the punctured DC subcarriermay be 73 or 72.

In step S200, the BS communicates with the low cost UE by using theallocated resource blocks. The communicating with the low cost UE byusing the allocated resource blocks may comprise transmitting a SIB tothe low cost UE by using the allocated resource blocks. In this case, alocation of the allocated resource blocks may be fixed.

Further, description of the present invention described above may beapplied to the embodiment of FIG. 28.

FIG. 29 shows a wireless communication system to implement an embodimentof the present invention.

An eNB 800 may include a processor 810, a memory 820 and a transceiver830. The processor 810 may be configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 810. The memory 820 is operatively coupled with the processor810 and stores a variety of information to operate the processor 810.The transceiver 830 is operatively coupled with the processor 810, andtransmits and/or receives a radio signal.

A low cost UE 900 may include a processor 910, a memory 920 and atransceiver 930. The processor 910 may be configured to implementproposed functions, procedures and/or methods described in thisdescription. Layers of the radio interface protocol may be implementedin the processor 910. The memory 920 is operatively coupled with theprocessor 910 and stores a variety of information to operate theprocessor 910. The transceiver 930 is operatively coupled with theprocessor 910, and transmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The transceivers 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What is claimed is:
 1. A method for transmitting system information fora narrowband user equipment (UE) by a base station (BS) in a wirelesscommunication system, the method comprising: determining a frequencylocation of a first narrowband for the narrowband UE based on a cellidentifier (ID), a system bandwidth, and information related to a firstsubframe; determining a frequency location of a second narrowband forthe narrowband UE based on the cell ID, the system bandwidth, andinformation related to a second subframe; and transmitting the systeminformation for the narrowband UE via the first narrowband in the firstsubframe and via the second narrowband in the second subframe.
 2. Themethod of claim 1, wherein the frequency locations of the firstnarrowband and the second narrowband are different from each other. 3.The method of claim 1, wherein the system information for the narrowbandUE is a system information block type-1 (SIB1) for the narrowband UE. 4.The method of claim 1, wherein the frequency locations of the firstnarrowband and the second narrowband are determined further based on atleast one of a subframe index or a system frame number (SFN).
 5. Themethod of claim 1, wherein each of the first narrowband and secondnarrowband include six physical resource blocks (PRBs).
 6. The method ofclaim 1, wherein the system information is transmitted via a physicaldownlink shared channel (PDSCH), and wherein the PDSCH is repeatedperiodically in every period of specific radio frames.
 7. A base station(BS) in a wireless communication system, the BS comprising: a memory; atransceiver; and a processor, coupled to the memory and the transceiver,that: determines a frequency location of a first narrowband for thenarrowband UE based on a cell identifier (ID), a system bandwidth, andinformation related to a first subframe, determines a frequency locationof a second narrowband for the narrowband UE based on the cell ID, thesystem bandwidth, and information related to a second subframe, andcontrols the transceiver to transmit the system information for thenarrowband UE via the first narrowband in the first subframe and via thesecond narrowband in the second subframe.
 8. The BS of claim 7, whereinthe frequency locations of the first narrowband and the secondnarrowband are different from each other.
 9. The BS of claim 7, whereinthe system information for the narrowband UE is a system informationblock type-1 (SIB1) for the narrowband UE.
 10. The BS of claim 7,wherein the frequency locations of the first narrowband and the secondnarrowband are determined further based on at least one of a subframeindex or a system frame number (SFN).
 11. The BS of claim 7, whereineach of the first narrowband and second narrowband include six physicalresource blocks (PRBs).
 12. The BS of claim 7, wherein the systeminformation is transmitted via a physical downlink shared channel(PDSCH), and wherein the PDSCH is repeated periodically in every periodof specific radio frames.